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Watch This Bacterium Use a Tiny Tentacle to Harpoon DNA

June 21, 2018

Written byAshley Hamer

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You can know all sorts of things about how microscopic creatures behave, but there's nothing like seeing it with your own eyes. Scientists knew bacteria possessed tiny appendages they used to navigate the world, but it wasn't until this month, when researchers released the footage below, that they saw it happen.

Cholera Me Ishmael

What you're seeing above is a bacterium snatching a fragment of DNA using an appendage called a pilus (plural: pili), which is more than 10,000 times thinner than a human hair. The image on the right shows the bacteria and pilus in green and the DNA in red; the image on the left shows the same cells without fluorescent dyes. While the general public may not have realized that bacteria have freakin' fishing lures built into their single-celled bodies, scientists were well aware — they had just never seen it in action. And they certainly didn't know exactly how these little harpoons caught DNA.

To capture this jaw-dropping footage, scientists from Indiana University used a method they described last year that involves dyeing the subjects — both bacterium and DNA — with special glowing hues. The bacterium they used was Vibro cholerae: the microbe that causes cholera.

Cholera is bad, but this is worse: What the bacterium is doing in that footage is what helps it build antibiotic resistance. Every piece of DNA it snatches can be incorporated into its own genome through what's called horizontal gene transfer, which helps them build stronger defenses to their attackers. As LiveScience's Rafi Letzter put it, "This would be a bit like if a person who's allergic to pollen needed only to reach out, snatch some loose flesh from a nonallergic friend and swallow it to get through spring without sneezing."

The pili shoot through incredibly small pores in the cell wall and spear a piece of DNA with a marksman's accuracy, right at its very tip. Finally, they reel the DNA back in. "It's like threading a needle," Indiana University Ph.D. student and first author Courtney Ellison said in a statement about the study, which was published this month in Nature Microbiology. "The size of the hole in the outer membrane is almost the exact width of a DNA helix bent in half, which is likely what is coming across. If there weren't a pilus to guide it, the chance the DNA would hit the pore at just the right angle to pass into the cell is basically zero."

Understanding more about how bacteria behave and adapt to their environments can help scientists make even greater strides in their fight against antibacterial resistance. With this new imaging method, these and other researchers can delve into other bacterial functions — maybe one of which could prove to solve the problem for good.